Rotary actuators produce oscillating power by rotating an output shaft through a fixed arc. They are compact, simple, and efficient. They produce high instantaneous torque in either direction and require only a small space and simple mountings.
The helical-spline actuator has a long, slender configuration and uses a sliding helical splined gear operating concept to convert linear piston motion into shaft rotation. It is composed of a cylindrically shaped housing and two moving parts: the shaft and the annular piston sleeve. Helical spline teeth machined on the shaft engage a matching complement of splines on the inside diameter of the piston. The outside diameter of the piston sleeve carries a second set of helical splines that engages a ring gear integral with the housing.
The piston sleeve is hydraulically sealed between the housing and shaft. When hydraulic pressure is applied to the port to the left of the piston, three events occur simultaneously. The piston sleeve is displaced axially, moving to the right; it rotates clockwise (as viewed from the output shaft) as the gearing on its outside diameter and the housing's ring gear forces its rotation; and the gearing on the inside diameter of the piston sleeve causes the shaft to rotate clockwise. Applying pressure to the alternate port returns the piston sleeve to its original starting position and rotates the shaft counterclockwise.
The double helix, opposite hand design of the gear sets compound the rotation of the shaft, so its rotation is considerably more than that of the piston sleeve. For 30° helix designs, the rotation of the shaft is almost twice that of the piston sleeve, for 45° helix designs, it is even more. Features of this design include high torque from a compact configuration, constant torque through full angle of rotation, no internal leakage, and holding torque approximately two times the forward driving torque.
Since the angle of rotation is determined by actuator length, and because there are no internal barriers as in vane designs, any rotation is theoretically possible. Conversely, an appropriate internal stop tube can limit the rotation of an actuator to almost any intermediate angle. Most helical actuators, however, are available with 90°, 180°, and 360° rotations as standard.
Problems do exist with standard helical rotary actuators. The torque output of helical actuators is a function of the working area of the actuator. The working area is the area between the diameter of the interior wall of the housing that the piston sleeve rides in and the diameter of the shaft that the piston rides on. Currently, the shaft has to be stepped to create a shoulder that a bearing rides against. However, by creating the shoulder, the diameter of the shaft must be greater. The diameter of the output shaft that protrudes out of the actuator is smaller than the diameter of the shaft that the piston rides on. As the housing diameter is kept constant to provide the smallest actuator possible, this reduces the amount of working area that an actuator can have. Therefore, the amount of torque output is limited by the diameter of the housing itself.
Additionally, the shaft output is generally splined to allow for attaching the actuator to a separate external member. For output shafts that are splined, the splines are not all the way up to the edge because the tool that cuts the splines needs clearance. This means that the hub that is inserted on the shaft is not supported the whole way, which creates the ability for it to be less stable and wobble and cause wear.
Therefore, there is a need in the art to provide a fluid powered, helical rotary actuator that is compact in size, but that produces a high torque output. There is also a need in the art for a smaller helical rotary actuator that produces the same torque output as is currently required. Additionally, there is a need in the art to protect the splined output shafts of helical rotary actuators and to help stabilize the output rotation.
It is therefore a primary object, feature, and/or advantage of the present invention to overcome or improve on deficiencies in the art.
It is another object, feature, and/or objective of the present invention to provide an improved helical rotary actuator that increases the working area of the actuator.
It is another object, feature, and/or advantage of the present invention to provide an improved helical rotary actuator that produces a greater torque output without increasing the size of the actuator.
It is another object, feature, and/or advantage of the present invention to provide an improved helical rotary actuator that uses a shaft with the same diameter for the piston sleeve and the output portions.
It is another object, feature, and/or advantage of the present invention to provide an improved helical rotary actuator that provides a greater stabilized connection between the output shaft and a hub.
It is another object, feature, and/or advantage of the present invention to provide an improved helical rotary actuator that provides protection for the output shaft for dealing with increased torque thrusts.
These and/or other objects, features, and advantages of the present invention will be apparent to those skilled in the art. The present invention is not to be limited to or by these objects, features and advantages. No single embodiment need provide each and every object, feature, or advantage.